System and method for interrupting a transmitting device in a communication system

ABSTRACT

A system and method for interrupting a transmitting device during a call. In the system, calls are transmitted from a first device on a communication channel as a series of channel frames. At predetermined times during the transmission, the transmitting device is configured to drop channel frames, resulting in open channel frame periods where the transmitting device is not transmitting on the communication channel. During these open channel frame periods, the transmitting device is also configured to switch to a receiving mode. Other devices in the system are capable of switching into a transmitting mode during the open channel frame periods and, when applicable, sending an interrupt request on the communication channel to the transmitting device in order to request access to the channel.

The present invention is a continuation application of U.S. patentapplication Ser. No. 13/296,375 filed in the United States Patent Officeon Nov. 15, 2011, the entire contents of which is incorporated herein byreference.

TECHNICAL FIELD OF THE DISCLOSURE

This disclosure relates generally to communication systems, and moreparticularly, to a system and method for interrupting a transmittingdevice in a communication system.

BACKGROUND OF THE DISCLOSURE

Wireless communication systems (e.g., time division multiple access(TDMA) systems, frequency division multiple access (FDMA) systems, orthe like) generally comprise a set of radios and a set of base stations.The radios, which may be mobile radios, portable radios or the like, aregenerally the endpoints of a communication path, while base stations aretypically stationary intermediates by which a communication path to aradio device is established or maintained.

When a subscriber is transmitting communications, there may be instanceswhen interrupting the transmitting subscriber may be important. Forexample, a first police officer needing back up may need to interrupt asecond police officer that is engaged in a call. In such an instance, itwould be important to have a mechanism to interrupt the second policeofficer to notify the second officer that the first police officerrequires assistance.

Accordingly, there is a need for interrupting a transmittingsubscriber/device in a communications system.

BRIEF DESCRIPTION OF THE FIGURES

Various embodiment of the disclosure are now described, by way ofexample only, with reference to the accompanying figures.

FIG. 1 illustrates an example of a communication system in accordancewith an embodiment of the present disclosure.

FIG. 2 illustrates a TDMA signal that may be used to transmit callinformation in the system of FIG. 1 in accordance with an embodiment ofthe present disclosure.

FIG. 3 illustrates a multi-burst call signal structure in accordancewith an embodiment of the present disclosure.

FIG. 4 illustrates a method for transmitting a TDMA call signal inaccordance with an embodiment of the present disclosure.

FIG. 5 illustrates a method for generating the TDMA call signal inaccordance with an embodiment of the present disclosure.

FIG. 6 illustrates a method for receiving the TDMA call signal inaccordance with an embodiment of the present disclosure.

FIGS. 7A-7C illustrate a method for interrupting a transmitting deviceoperating in repeater mode in accordance with an embodiment of thepresent disclosure.

FIG. 8 illustrates a method for interrupting a transmitting deviceoperating in direct mode in accordance with an embodiment of the presentdisclosure.

FIG. 9 illustrates an example of a link control message in accordancewith an embodiment of the present disclosure.

FIG. 10 illustrates an example of an interrupt request in accordancewith an embodiment of the present disclosure.

FIG. 11 illustrates a method for transmitting a FDMA call signal inaccordance with an embodiment of the present disclosure.

FIG. 12 illustrates a method for generating the FDMA call signal inaccordance with an embodiment of the present disclosure.

FIG. 13 illustrates a method for receiving the FDMA call signal inaccordance with an embodiment of the present disclosure

Skilled artisans will appreciate that elements in the figures areillustrated for simplicity and clarity and have not necessarily beendrawn to scale. For example, the dimensions and/or relative positioningof some of the elements in the figures may be exaggerated relative toother elements to help improve the understanding of various embodimentsof the present disclosure. Also, common but well-understood elementsthat are useful or necessary in a commercially feasible embodiment arenot often depicted in order to facilitate a less obstructed view ofthese various embodiments of the present disclosure. It will be furtherappreciated that certain actions and/or steps may be described ordepicted in a particular order of occurrence while those skilled in theart will understand that such specificity with respect to sequence isnot actually required. It will also be understood that the terms andexpressions with respect to their corresponding respective areas ofinquiry and study except where specific meaning have otherwise been setforth herein.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure provides a system and method for interrupting atransmitting device during a call. In accordance with this disclosure,calls are transmitted from a first device on a communication channel asa series of channel frames, which may be, for example, a series ofbursts in a TDMA system, a series of payload frames in an FDMA, and thelike. At predetermined times during the transmission, the transmittingdevice is configured to drop channel frames, resulting in open channelframe periods where the transmitting device is not transmitting on thecommunication channel. During these open channel frame periods, thetransmitting device is also configured to switch to a receiving mode.

Other devices in the system, such as any radios or base stationsreceiving the call, are then capable of ascertaining the timing of theopen channel frame periods and switching into a transmitting mode duringthe open channel frame periods. If another device in the system needs tointerrupt the transmitting device, that other device is configured tosend an interrupt request on the communication channel to thetransmitting device in order to request access to the channel. Uponreceiving the interrupt request, the transmitting device ceases orpauses transmission, allowing the other device to then begintransmitting a new call on that same communication channel.

Let us now discuss the present disclosure in greater detail by referringto the figures below. FIG. 1 illustrates an exemplary communicationsystem 100 that may be used for implementing the present disclosure.Communication system 100 comprises mobile communication devices 102,104, and 106, which may be for example, portable or mobile radios,personal digital assistants, cellular telephones, video terminals,portable computers with a wireless modem, or any other wireless devices.For purposes of the following discussions, the communication devices maybe referred to as “radios”, but they are also referred to in the art assubscribers, mobile stations, mobile equipment, mobiles, portables,handsets, etc.

Radios 102, 104, and 106 communicate over a radio access network 108 viawireless communication resources. Of course, those of ordinary skill inthe art will realize that any type of network is within the scope of theteachings herein. Thus, the radio access network 108 may compriseinfrastructure such as, but not limited to, base stations (with a singlebase station 110 shown for clarity), base station controllers (notshown), network elements (such as a mobile switching center, homelocation register, visitor location register, etc.), and the like, tofacilitate the communications between radios having access to the radioaccess network 108. As shown in FIG. 1, base station 110 may also beconfigured to communicate with one or more dispatch console sites 118.

The wireless communication resources used for communication between thebase station 110 and radios 102, 104, and 106 may include any type ofcommunication resource such as, for example, radio frequency (RF)technologies, including, but not limited to TDMA; Code Division MultipleAccess (CDMA), FDMA, Orthogonal Frequency Division Multiple Access(OFDMA) and the like. Other wireless technologies, such as those nowknown or later to be developed and including, but not limited to,infrared, Bluetooth, electric field, electromagnetic, or electrostatictransmissions, may also offer suitable substitutes.

In the illustrated communication system 100, radios 102, 104, and 106may communicate with one another either in “repeater mode” or in “directmode.” In repeater mode, the radios 102, 104, and 106 may communicatewith each other by radio 102 establishing a wireless link or radioconnection 112 with base station 110 over an available RF channel, radio104 establishing a wireless link 114 with base station 110 over anavailable RF channel, and radio 106 establishing a wireless link 116with base station 110 over an available RF channel. As is wellunderstood in the art, base station 110 comprises one or more repeaterdevices that receive a signal from one of the radios 102, 104, or 106over the respective link 112, 114, or 116 and retransmit the signal toone or more of the other radios. Communication from a radio 102, 104, or106 to base station 110 are generally referred to as being inbound whilecommunications from base station 110 to a radio 102, 104, or 106 aregenerally referred to as being outbound.

As also shown in FIG. 1, in direct mode (also commonly referred to astalkaround mode), radios (e.g., radios 102 and 106) may communicatedirectly, without a base station, by establishing a wireless link withone another. As will be understood from the discussions below, thepresent disclosure is equally applicable to both direct modecommunications and communications via base station 110.

Of course, while one embodiment of a communication system is illustratedin FIG. 1, practitioners skilled in the art will appreciate that thesystem 100 may also include various other elements not shown in FIG. 1.For example, while only three radios and one base station is shown forease of illustration, those skilled in the art will realize that in atypical system a much larger number of radios are supported by a radionetwork. The system 100 may also include many more base stations than isshown in FIG. 1.

One exemplary embodiment of the present disclosure is illustrated inFIGS. 2-10. This illustrated embodiment is described with reference to aTDMA system compliant with European Telecommunications Institute (ETSI)standards TS 102 361. However, one skilled in the art should understandthat the present disclosure may similarly be applied to other TDMAsystems or any other type of communication system that is configured totransmit calls as a series of channel frames. For example, the presentdisclosure may equally be applied to an FDMA system compliant withETSI-dPMR standard (ETSI TS 102 490).

Turning first to FIG. 2, one exemplary embodiment of a TDMA carriersignal 200 that may be used for transmitting information in accordancewith the present disclosure is illustrated. Generally, each TDMA carriersignal 200 is divided into numerous time slots or communication streams.In FIG. 2, the TDMA carrier signal 200 is illustrated having two timeslots, labeled respectively as “1” and “2”, although it should beunderstood that a TDMA carrier signal in accordance with the presentdisclosure could also have any number of time slots, such as 4, 8, 16 orany other potential number of time slots.

Each time slot includes discrete information packets 202 and 204 (alsoreferred to herein as “bursts” or more generically as “channel frames”)configured to carry a specific amount of information. As shown in FIG.2, sub-slots 206 may also be provided between each of the bursts. Foroutbound signals, the sub-slots 206 typically include a CommonAnnouncement Channel (CACH) signal. For inbound signals, the sub-slots206 typically provide guard time between bursts.

When calls are initiated, they are assigned to a communication channel.In a TDMA system, the communication channel may be comprised of one ormore time slots. For example, when operating in repeater mode, eachcommunication channel may be comprised of one or more time slots fortransmitting the call from a radio to the base station (i.e., an inboundchannel link), and one or more time slots for transmitting the call fromthe base station (i.e., an outbound channel link). In direct mode, onthe other hand, only one channel link is generally required to transmitthe call.

FIG. 3 illustrates one example of a multi-burst structure for a TDMAcall signal, in accordance with protocols set out in ETSI standard TS102 361, that may be utilized to transmit call information on a TDMAcarrier signal 200. In this embodiment, the TDMA call signal 300 isseparated into multiple superframes 302. Each superframe 302 includessix individual bursts A, B, C, D, E, and F, each of which is 27.5 ms induration. Every 360 ms during a call, this superframe burst sequence isrepeated.

Each voice call may also begin with a header 304. The header 304 mayinclude a link control header burst, which may contain information, suchas a manufacturer ID, a talkgroup ID, a source ID, and a destination ID.It should also be understood that header 304 may be comprised ofmultiple header bursts, each containing different types of information.

As further shown in FIG. 3, each burst A-F includes a payload field 306,an EMB field 308 and an embedded signaling field 310. The payload field306 includes the particular media information being transmitted (i.e.,voice, data, control, video, etc.) and is comprised of three informationframes: IF1, IF2, and IF3. As can be seen from FIG. 3, the secondinformation frame, IF2, is split into two parts, one on either side ofthe embedded signaling field 310. When transmitting voice callinformation, each information frame in bursts A-F corresponds to 20 msof voice information.

The embedded signaling field 310 may include synchronization and othercontrol data. In one embodiment, the embedded signaling field 310 ofburst A includes a voice frame synchronization signal, while theembedded signaling fields of the remaining bursts include Link Controlinformation or other signaling information. Such synchronization andsignaling information may be comprised of various information elementsas are well known in the art. The EMB field 308 includes informationelements that define the meaning of the payload field. For example, inaccordance with ETSI standard TS 102 361, the EMB field 308 may includeinformation elements such as color code information, link control startstop (LCSS) bits, a privacy bit, and EMB parity.

In accordance with the present disclosure, a communication device thatis in the process of transmitting a call (also referred to as a“transmitting device”) is configured to periodically or intermittentlydrop channel frames (i.e., bursts in a TDMA system or payload frames inan FDMA system) during transmission. Thus, the transmitting device isconfigured to not transmit a channel frame during a predetermined set ofchannel frame periods. During these predetermined channel periods, thetransmitting device is also configured to switch over into a receivingmode in order to listen for any incoming transmissions. For purposes ofthis disclosure, a channel period during which a transmitting devicedoes not transmit a frame is referred to as an “open channel frameperiod.” In the case of a TDMA system, an open channel frame period mayalso be referred to as an “open burst period.” Similarly, in the case ofan FDMA system, an open channel frame period may also be referred to asan “open payload frame period.” It should also be understood that theterm “call” is meant to include any type of multimedia transmission, aswell as transmissions comprising system control information.

Communication devices that are in the process of receiving the call(also referred to as “receiving devices”) may also be configured toswitch, when necessary, into a transmitting mode in order to initiatetransmissions during an open channel frame period. As will be explainedin further detail below, this permits non-transmitting devices in thecommunication system to send interrupt requests to the transmittingdevice in order to request use of the channel being utilized by thetransmitting device, and permits the transmitting device to receive suchinterrupt requests while transmitting.

FIG. 4 illustrates one exemplary embodiment for transmitting a TDMA callsignal in accordance with the present disclosure. In this embodiment,the transmitting device is configured to drop a burst every thirdsuperframe, and more particularly, to drop an F burst during every thirdsuperframe. That is, the transmitting device does not transmit the Fburst from every third superframe. Each open burst period in FIG. 4 isillustrated using the letters “Dr” to indicate that no burst wastransmitted during that burst period. For purposes of this description,each set of three superframes is also identified as superframes 1, 2,and 3, with superframe 3 having the open burst period.

In the embodiment discussed in FIG. 4, the F burst is dropped because,in accordance with the signaling structure described in FIG. 3, the Fburst generally includes the least significant control information ascompared to other bursts in the superframe. However, it is understoodthat other bursts in the superframe may also be selected to be dropped.The transmitting device may also be configured to alternate droppingdifferent bursts in the superframes.

It should also be understood that the duration between dropped burstsmay be altered as a matter of design choice. Increasing the durationbetween dropped bursts decreases the amount of call information that islost from the transmission but also increases the amount of time betweenopportunities when a non-transmitting device can request access to thechannel, and vice-versa. For example, in the embodiment described abovefor a 2-slot TDMA system, a burst is dropped every third superframe and,therefore, the time between open burst periods is 1080 ms. If the burstis alternatively dropped every sixth superframe, the call quality may beincreased but the time between open burst periods would be increased to2160 ms.

In one exemplary embodiment, the transmitted call signal may also employsignaling to identify the timing of the open burst period. For example,in the embodiment described in FIG. 4, the transmitted link controlinformation may transmit certain information during the superframe priorto the superframe which will provide the open burst period (i.e.,superframe 2 in FIG. 4) to indicate that the next superframe willcontain an open burst period. The transmitted call signal may alsotransmit information to indicate that the transmitted signal isutilizing burst dropping in its transmission, which allows receivingdevices to determine whether the transmitting device can be interruptedusing the process described herein. This is especially useful in acommunication system in which only a portion of the devices areconfigured to operate using the present disclosure. This information maybe transmitted during a header burst 304, in the link controlinformation of each burst, or as any other type of message.

One exemplary embodiment of link control message that may be utilized toperform both of the functions in the TDMA system described above isillustrated in FIG. 9. In this embodiment, the link control message 900includes a service options field 902, which further includes a BurstDropping (BD) information element 904, and a Penultimate Superframe (PS)information element 906. The BD information element 904 is comprised ofa single bit that is set to the value 1 if the transmitting device isdropping bursts while transmitting. The PS information element 906 isalso comprised of a single bit that is set to the value 1 during thesuperframe immediately preceding a superframe having an open burstperiod (i.e., a superframe 2 in FIG. 4), and set to the value 0 duringall other superframes. The link control message 900 may also include aFeature Set ID (“FID”) information element 910. The FID informationelement 910 may include a standard ID if the transmitted call is notusing dropping bursts, or may include a proprietary ID if thetransmitted call is dropping bursts. In one embodiment, the proprietaryID may be a manufacturer's ID. The remaining information elementsillustrated in the link control message are well known and are thereforenot discussed in any further detail herein. It should also be understoodthat this link control message 900 is but one example. Thus, therelevant information elements may be provided in different portions ofthe link control message 900. Other information elements in the linkcontrol message 900 may also be used to provide similar functionality.For example, rather than using a BD information element 904 or FIDinformation element 910, the OPCODE information element 908 mayadditionally or alternatively be configured to indicate that thetransmission is using burst dropping.

FIG. 5 illustrates one exemplary embodiment for generating, at atransmitting device, the signaling structure in FIG. 4. In thisembodiment, the bursts are generated so as to minimize the impact of thedropped burst on the call quality. As noted above, each burst iscomprised of three information frames, each of which is encoded with apredetermined amount of call information (e.g., 20 ms of voiceinformation for voice calls). Thus, the six bursts A-F that make up eachsuperframe are typically comprised of a total of eighteen informationframes (e.g., 360 ms of voice information for voice calls). In FIG. 5,fifty-four information frames, numbered 1 through 54, for threeconsecutive superframes 1-3 are illustrated.

In this embodiment, one information frame is discarded at the end ofeach superframe. Thus, as shown in FIG. 5, bursts A-F in superframe 1are generated using information frames 1-18. Information frame 19 isthen discarded and bursts A-F for superframe 2 are generated usingbursts 20-37. Following superframe 2, information frame 38 is discardedand bursts A-E of superframe 3 are generating using information frames39-53. Information frame 54 is then also discarded, and the F burst forsuperframe 3 is dropped (i.e., the F burst is not transmitted, but thechannel timing remains intact, thus leaving an open burst period). Thisprocess is repeated for each series of three superframes. As a result,the effect of the dropped burst on the quality of a call, and inparticular a voice call, is diminished because only a single informationframe is lost from each superframe.

Of course, it should be understood that this is only one exemplarymethod for generating the signaling structure of FIG. 4. For example,any of the information frames may be chosen to be discarded for eachsuperframe. If call quality is not a concern, the communication devicemay also be configured to simply generate the first two superframesusing information frames 1-36, generate the third superframe usinginformation frames 37-51, and then discard information frames 52-54.

To enable seamless generation of bursts while discarding certaininformation frames, the call information may also be buffered by apredetermined amount of time prior to initiating transmission. Forexample, in the embodiment described above in which three 20 msinformation frames are to be discarded every three superframes, it wouldbe desirable to provide at least a 60 ms buffer before initiatingtransmission.

FIG. 6 illustrates one exemplary embodiment for receiving a call that istransmitted using the methods shown in FIGS. 4 and 5. When each burstA-F is received, the receiving device extracts the information framesfrom each received burst in order to provide the encoded callinformation to the user. Thus, as shown in FIG. 6, information frames1-3 are extracted from burst A in superframe 1, information frames 4-6are then extracted from burst B in superframe 1, and so on.

At the end of each superframe, to account for the discarded informationframe, the receiving device plays a mitigated information frame beforebeginning the next superframe. Thus, as shown in FIG. 6, after receivinginformation frames 1-18 in superframe 1, the receiving device plays amitigated information frame 19. Similarly, after receiving informationframes 20-37 for superframe 2, the receiving device plays a mitigatedinformation frame 38; and after receiving information frames 39-53, thereceiving device plays a mitigated information frame 54. This process isthen repeated for each series of three superframes.

The mitigated information frames may be generated using varioustechniques known in the art. For example, in one embodiment, a mitigatedinformation frame may be generated by interpolating between theinformation frames received immediately before and after the time when amitigate information frame is to be inserted. In another embodiment, amitigated information frame may be generated by repeating the priorinformation frame. In another embodiment, a mitigated information framemay be generated by playing the subsequently received information frametwice. In yet another embodiment, the mitigated information frame maysimply be a muted frame.

FIGS. 7A-7C illustrate one exemplary embodiment of a method by which anon-transmitting device may interrupt a transmitting device inaccordance with the present disclosure. More particularly, FIGS. 7A-7Cdescribe an embodiment in which a non-transmitting device (i.e., an“interrupting device”) needs to interrupt a transmitting device that istransmitting a call via a base station 110 in repeater mode. As anexample, let us assume that in the communication system 100 of FIG. 1,radio 102 is the transmitting device and radio 104 is the interruptingdevice.

The various blocks shown in FIGS. 7A-7C indicate transmission of thevarious bursts and signals from the respective communication devices.Thus, the transmitting device 102 is illustrated transmitting a seriesof TDMA bursts to a base station 110 on a first TDMA time slot (i.e. the“inbound channel link”). Each burst is received by the base station 110and retransmitted during a subsequent burst period to othercommunication devices on another TDMA time slot (i.e., the “outboundchannel link”). Thus, burst “A” is transmitted from the transmittingdevice 102, received by the base station 110, and retransmitted duringthe next available burst period on the outbound channel link. The sameprocess is then performed for each subsequent burst. As a result, inthis embodiment, bursts are typically transmitted to other communicationdevices in the system one burst period after the burst has beentransmitted from the transmitting device.

As discussed above, the transmitting device 102 is also configured toperiodically drop a burst during transmission. During an open burstperiod 702, when the base station 110 does not receive a burst from thetransmitting device 102, the base station transmits an erasure burst 404on the following burst period of the outbound channel link to indicatethat no call information was received from the transmitting device. Theerasure burst 404 is typically comprised of three erasure informationframes. The structure and function of an erasure information frame thatis used for an erasure burst is well known in the art and is thereforenot discussed any further herein.

Turning to FIG. 7B, if an interrupting device 104 has determined thatthe transmitting device 102 is to be interrupted, the interruptingdevice 104 transmits, during an open burst period 702, an interruptrequest 706 on the inbound channel link. In one embodiment, theinterrupt request 706 may be sent automatically upon a user keying acall at the interrupting device 706. However, the interrupting devicemay also be configured with a transmitter interrupt button to permit theuser of the interrupting device to manually request transmission of theinterrupt signal. Upon transmitting an interrupt request, theinterrupting device 104 may also be configured to provide a userperceivable notification to the user to indicate that the interruptrequest 706 has been sent. The user perceivable notification may be anaudible signal, a visual cue, or any other type of notification that canbe perceived by the user.

There are various scenarios where it may be desirable to interrupt thetransmitting device. For example, it may be desirable to interrupt atransmitting device if another device needs to transmit an emergencycall. It may also be desirable to interrupt a transmitting device if ahigher-priority device needs to initiate a call. It may also bedesirable to interrupt a transmitting device if a non-transmittingdevice needs to send an urgent data message or an event indicator to thetransmitting device. If devices in the communication system areconfigured to permit remote monitoring (i.e., allowing one device toremotely activate the microphone of another device), it may also bedesirable to also remotely interrupt or dekey the device beingmonitored.

Of course, these are provided merely as examples, and it should beunderstood that there may be numerous other scenarios where it would bedesirable to interrupt the transmitting device. For instance, althoughthe illustrated interrupting device in FIGS. 7A-7C is a radio, it shouldbe understood that the interrupting device may be any other device. Asan example, the base station may be configured to transmit an interruptrequest to a transmitting device upon receiving a command from a consolesite or other device to interrupt the transmitting device. It shouldalso be understood that the interrupt request may be configured to causethe transmitting device to either completely cease transmitting or topause for a certain amount of time.

The base station 110, after receiving the interrupt request 706, maygenerate and transmit an acknowledgement signal 708 to the interruptingdevice 104 on the outbound channel link to indicate that the interruptrequest 706 had been received. In one exemplary embodiment, theacknowledgement signal 708 may be transmitted within an embeddedsignaling field of an erasure burst, although other message structuresmay also be used.

Turning to FIG. 7C, after transmitting the acknowledgment signal 708,the base station 110 begins broadcasting the interrupt request 706 onthe outbound channel link during the next superframe in which thetransmitting device is expected to drop a burst. In the illustratedembodiment, the interrupt request 706 is broadcast during each burstperiod (i.e., A-F) of the superframe in which an open burst period 402is expected (e.g., a superframe 3 in FIG. 4). Since the transmittingdevice 102 switches to a receive mode during the open burst period 402,the transmitting device 102 receives the interrupt request 706 duringthis open burst period 402. Any other device listening to the call alsoreceives the interrupt request 706, thus indicating to each such devicethat the transmitting device is about to be interrupted.

Of course, it will be understood that the number of times that theinterrupt request is actually transmitted by the base station 110 is amatter of design choice so long as at least one such transmissioncoincides with the open burst period 702. For example, increasing thenumber of times an interrupt request is transmitted increases thelikelihood that the interrupt request will be received by deviceslistening to the call, while decreasing the number of time an interruptrequest is transmitted decreases the amount of the transmitted call thatis truncated by the base station 110.

After receiving the interrupt request 706, the transmitting device 102takes an appropriate action based the received interrupt request. In theembodiment illustrated in FIG. 7C, the transmitting device 102 send anacknowledgement message 710 on the inbound channel link during the nextavailable burst period and then ceases transmitting. However, thetransmitting device 102 may also be configured to take other actionsdepending on the interrupt request received. For example, thetransmitting device may be configured to pause transmission for acertain amount of time. The transmitting device 102 may also beconfigured to provide a user perceivable notification to the user toindicate that an interrupt request has been received.

The base station 110, upon receiving the acknowledgment message 710,stops broadcasting the interrupt request, and transmits theacknowledgment message 710 on the outbound channel link to theinterrupting device 104. Once the interrupting device 104 receives theacknowledgement message 710, the interrupting device 104 beginstransmitting on the inbound channel link. If the call is a voice call,the interrupting device may also be configured to provide a userperceivable notification to the user to indicate that the interruptrequest has been acknowledged and to inform the user that they may beginspeaking.

Although not shown in FIG. 7C, the transmitting device 102 may also beconfigured to transmit multiple instances of an acknowledgement message710 after receiving an interrupt request 706 to decrease the risk of theacknowledgement message 710 being lost. In another embodiment, thetransmitting device 102 may also be configured to continue transmittingthe acknowledgement message 710 until it has been properly received bythe base station 110. For example, the transmitting device 102 may beconfigured to alternate between transmitting an acknowledgement message710 and listening to the outbound channel link until the transmittingdevice 102 determines that the base station 110 is no longerbroadcasting the interrupt request 706.

FIG. 8 illustrates another exemplary embodiment of the presentdisclosure in which a transmitting device is operating in direct mode.In this embodiment, each burst is transmitted directly from thetransmitting device 102 to each device listening to the call. In FIG. 8,let us assume that in the communication system 100 of FIG. 1, radio 102is the transmitting device and radio 106 is the interrupting device.Similarly, the transmitting device 102 is also configured toperiodically drop a burst during transmission.

In this embodiment, if an interrupting device 106 has determined thatthe transmitting device 102 is to be interrupted, the interruptingdevice 106 transmits, during an open burst period 802, an interruptrequest 804 to the transmitting device 102.

After receiving the interrupt request, the transmitting device 102 takesappropriate actions. In the embodiment shown in FIG. 8, this includestransmitting to the interrupting device 106 an acknowledgement message806 during the next available burst period and then ceasingtransmission. Upon receiving the acknowledgment message 806, theinterrupting device 106 begins transmitting.

As in the embodiment described in FIGS. 7A-7C, the transmitting device102 in FIG. 8 may also be configured to provide a user perceivablenotification upon receiving an interrupt request, and the interruptingdevice may be configured to provide a user receivable notification uponsending the interrupt request and/or receiving acknowledgement of theinterrupt request from the transmitting device. The transmitting devicemay also be configured to transmit the acknowledgement message multipletime to increase the chance of it being received, or to continuetransmitting the acknowledgement message until it is determined that theinterrupting device has received the acknowledgement message and beguntransmitting.

FIG. 10 illustrates one exemplary embodiment of an interrupt request 706that may be utilized in TDMA communication system described above. Inthis embodiment, the interrupt request 706 may in the form of a ControlSignaling Block (“CSBK”) message. As shown in FIG. 10, the interruptrequest 706 includes an interrupt type information element 1002. Theinterrupt type information element 1002 may be utilized to indicate thepurpose of the interrupt request. For example, in one embodiment, theinterrupt type information element 1002 may be comprised of 5 bits inwhich the value 00001 indicates interruption from a higher prioritycall, 00010 indicates interruption of by an emergency call, and 00011indicates interruption of a device that is being remotely monitored. Ofcourse, additional types of interrupt requests may also be provided forand any values may be used for each type. The interrupt type informationelement 1002 may also be configured to indicate whether the transmittingdevice is to cease transmitting or simply pause for a certain amount oftime.

The interrupt request 706 further includes a target address informationelement 1004 and a source address information element 1006. When theinterrupt request 706 is sent from an interrupting device, the targetaddress information element 1004 identifies the address of thetransmitting device to be interrupted, and the source addressinformation element 1006 identifies the device that is requesting accessto the channel. The remaining information elements shown in theinterrupt request are well known information elements utilized in CSBKsignals and are therefore not discussed in any further detail herein.

Further advantages and modifications of the above described system andmethod will readily occur to those skilled in the art. For example,while the present disclosure has been described with regards to anexemplary TDMA system, it is understood that the present disclosure isequally applicable any other type of system that transmits calls as aseries of channel frames. For instance, the TDMA call signal describedabove in FIGS. 4, 5, and 6 could easily be based upon the air interfaceprotocol described in the ETSI TS 102 361 standard (ETSI-DMR standard).In yet another embodiment of the present disclosure, an FDMA call signaldescribed below in FIGS. 11, 12 and 13 could easily be based upon theair interface protocol described in the ETSI TS 102 490 standard(ETSI-dPMR standard) and still remain within the spirit and scope of thepresent disclosure. For example, let us now briefly illustrate someexamples of an FDMA system and highlight the differences between theFDMA call signal and the TDMA call signal as described above. In anETSI-dPMR FDMA system, as illustrated in FIG. 11, FDMA call signals aretypically separated into superframes each having four payload framesA-D, with each payload frame having four information frames. In anETSI-dPMR FDMA system, payload frames may be periodically dropped tocreate open payload frame periods. Thus, in one exemplary embodiment,sufficient open payload frame periods may be produced by dropping apayload frame every fourth superframe in accordance with an embodimentof the present disclosure. In other words, an FDMA call signal havingsuperframes comprising four payload frames, one payload frame from everyfourth superframe is not transmitted in order to provide an interruptopportunity for another device. To minimize the impact on call quality,an information frame may also be discarded every 16 information framesso that only one information frame is discarded during each superframe.Thus, FIG. 12 illustrates a method for generating the FDMA call signalwith payload frames comprising four information frames and oneinformation frame of every sixteen information frames is discarded insuch a way to allow every sixteenth payload frame to not be transmittedin order to provide an interrupt opportunity for another device inaccordance with an embodiment of the present disclosure. Of course, aswith the TDMA embodiment described above, the rate of dropped payloadframes and/or the selected information frames to be discarded may bealtered. Additionally, FIG. 13 illustrates a method for receiving anFDMA call signal with payload frames comprising four information framesand one mitigated information frame is inserted after every sixteenreceived information frames in accordance with an embodiment of thepresent disclosure. It should be readily apparent to those skilled inthe art that other embodiments are possible which employ differentchannel frame dropping rates and different information frame droppingrates while using FDMA call signals, TDMA call signals, or other typesof call signal and still remain within the spirit and scope of thepresent disclosure.

The disclosure, in its broader aspects, is therefore not limited to thespecific details, representative system and methods, and illustrativeexamples shown and described above. Various modifications and variationscan be made to the above specification without departing from the scopeor spirit of the present disclosure, and it is intended that the presentdisclosure cover all such modifications and variations provided theycome within the scope of the following claims and their equivalents.

What is claimed is:
 1. A method for interrupting a transmitting devicetransmitting a call in a communication system, the method comprising: afirst device encoding call information of a call to be transmitted intoa series of channel frames; the first device operating in a transmittingmode and transmitting the call on a communication channel via the seriesof channel frames, and the first device inserting a plurality of openchannel frame periods on to the communication channel duringtransmission of the call by selectively dropping, instead oftransmitting, a corresponding predetermined plurality of the channelframes or portions of the channel frames; the first device switching toa receiving mode during one of the inserted open channel frame periodsand determining, while in the receiving mode, whether an interruptrequest has been transmitted from a second device and received at thefirst device; and responsive to the first device determining that aninterrupt request has been transmitted from the second device andreceived at the first device, as a function of the interrupt request, atleast one of: the first device ceasing transmitting of the call; and thefirst device pausing transmission of the call for a predetermined periodof time.
 2. The method of claim 1, wherein the first device is a radioand: the second device is a radio, and the interrupt request is receivedby the first device directly from the second device or from the seconddevice via a base station.
 3. The method of claim 1, wherein: the callis transmitted as a series of superframes, each superframe having one ormore channel frames, the plurality of open channel frame periods areprovided periodically during transmission of the call, and an openchannel frame period is provided once every x superframes transmittedduring the call, wherein x is an integer greater than or equal to one.4. The method of claim 3, wherein each of the series of channel framesis comprised of a predetermined number of information frames and whereinthe method further includes, in the transmitting mode: encoding a seriesof information frames; generating the series of channel frames from theseries of information frames; and periodically discarding a particularinformation frame while generating the series of channel frames.
 5. Themethod of claim 4, wherein one information frame is discarded aftertransmission of each superframe.
 6. The method of claim 1, furtherincluding transmitting an acknowledgment message acknowledging receiptof the interrupt request to the second device after receiving theinterrupt request.
 7. The method of claim 1, wherein the communicationsystem is one of the following: a time division multiple access (TDMA)system and the call is transmitted as a series of bursts; and afrequency division multiple access (FDMA) system and the call istransmitted as a series of payload frames.
 8. The method of claim 1,further comprising embedding an indication in a channel frame, prior toeach open channel frame period, of when the next open channel frameperiod will occur.
 9. The method of claim 1, wherein the at least one ofthe dropped channel frames or portions of the channel frames includescall audio data.
 10. The method of claim 1, wherein the at least one ofthe dropped channel frames or portions of the channel frames includescall control information.
 11. A method for interrupting a transmittingdevice in a communication system, the method comprising: a first deviceoperating in a receiving mode and receiving a first call on acommunication channel via a series of channel frames, and wherein aplurality of open channel frame periods are inserted on to thecommunication channel during transmission of the call by a second deviceselectively dropping, instead of transmitting, a correspondingpredetermined plurality of the channel frames or portions of the channelframes; the first device mitigating the dropped correspondingpredetermined plurality of the channel frames or portions of the channelframes caused by the second device's insertion of the open channel frameperiods; the first device determining that the first call beingtransmitted by the second device must be interrupted; the first deviceswitching from operating in the receive mode to operating in a transmitmode during one of the open channel frame periods inserted by the seconddevice; the first device, while in the transmit mode and during the oneof the open channel frame periods, transmitting an interrupt request tothe second device; and after transmitting the interrupt request, thefirst device transmitting a second call on the communication channel.12. The method of claim 11, further including the first devicedetermining whether an acknowledgment of the interrupt request has beenreceived from the second device, and the first device transmitting thesecond call responsive to receiving the acknowledgement.
 13. The methodof claim 11, further comprising determining a next open channel frameperiod from information embedded in one or more received channel framesof the call; wherein the step of switching the first device from thereceive mode to a transmit mode is executed during the determined nextopen channel frame period.
 14. A system for interrupting a transmittingdevice transmitting a call in a communication system comprising: a firstdevice configured to: encode call information of a call to betransmitted into a series of channel frames; operate in a transmit modeand transmit a first call on a communication channel via the series ofchannel frames; insert a plurality of open channel frame periods on tothe communication channel during transmission of the first call byselectively dropping, instead of transmitting, a correspondingpredetermined plurality of the channel frames or portions of the channelframes; switch to a receive mode during at least one of the insertedplurality of open channel frame periods; and receive a call interruptrequest from a second device and, as a function of the interruptrequest, cease transmitting the call or pause transmitting the call fora predetermined amount of time; a second device configured to: receivethe first call on the communication channel; mitigate the droppedcorresponding predetermined plurality of the channel frames or portionsof the channel frames caused by the second device's insertion of theopen channel frame periods; determine that the first call beingtransmitted by the first device must be interrupted and responsivelyswitch to a transmitting mode during one of the open channel frameperiods inserted by the second device and transmit the call interruptrequest to the first; and after transmitting the call interrupt request,transmit a second call on the communication channel.
 15. The method ofclaim 1, wherein the call is transmitted directly from the first deviceto the second device.
 16. The system of claim 14, wherein the firstdevice is further configured to embed an indication in a channel frame,prior to each open channel frame period, of when the next open channelframe period will occur.
 17. The system of claim 14, wherein the atleast one of the dropped channel frames or portions of the channelframes includes call audio data, and wherein the second device isconfigured to mitigate the dropped call audio data.